System and method for transmitter leak-over cancellation

ABSTRACT

The present disclosure relates generally to systems and methods for transmitter leak-over cancellation. In one example, a method includes transmitting a signal via a transmit chain in a wireless device, where a portion of the signal leaks over into a receive chain of the wireless device and generates higher order products that interfere with a signal being received by the wireless device. A portion of the signal from the transmit chain is diverted into cancellation circuitry coupled to the receive chain prior to a location in the transmit chain where leak-over occurs, and an amplitude and phase of the portion is manipulated. The manipulated portion is combined with the received signal and other portion to at least partially cancel interference caused by the portion leaking over into the receive chain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Patent Application Serial No.(Attorney Docket No. 2006.06.019.WS0/1005.27), filed on Feb. 16, 2007,and entitled “SYSTEM AND METHOD FOR TRANSMITTER LEAK-OVER CANCELLATIONUSING CLOSED LOOP OPTIMIZATION”, which is hereby incorporated byreference.

BACKGROUND

Some wireless communication devices, such as those based on frequencydivision duplexing (FDD), are designed to simultaneously transmit andreceive signals using two or more frequency channels. Such simultaneoustransmission and reception may inherently introduce a modulatedinterferer in the transmit channel frequency at the receiver input(e.g., leak-over of the signal being transmitted from a transmit chainof the device into a receive chain). Such FDD devices generally use aduplexer to isolate between the signals being transmitted and thereceiver, and the leak-over at the duplexer may depend on its isolationperformance in the transmit band. Traditionally, a high degree ofisolation is provided at the duplexer to minimize the leak-over of themodulated transmit signal.

FDD receivers with a direct conversion architecture are generallydesigned with an external inter-stage filter solely to reduce the impactof the transmit leaked-over interferer signal on a first mixer withinthe receive chain even though there is no image frequency. This mayimpose a fairly severe limitation on radio receivers supportingmulti-band operations, as not only is a duplexer required at each bandto provide the needed transmit band isolation (e.g., of 55 dB), but aninter-stage external filter is also needed for each band. Accordingly,the support of multiple bands imposes a large number of radio frequency(RF) input/output (I/O) demands on a radio frequency integrated circuit(RFIC) integrated with a low noise amplifier (LNA) in the receive chain.In some cases, multi-band RFICs are designed with a separate chip forthe LNA, which results in a multi-chip solution.

Besides the higher component count and restrictive RF I/O requirements,the transmit leak-over may force a different receive chain architecturefor TDD and FDD operational modes. The use of different architectures isforced partly because of the need for an inter-stage filter in FDDdesigns, which may result in the use of separate receivers in devices tosupport both TDD and FDD operational modes. The use of separatereceivers not only increases design complexity, but also uses more diearea on the RFIC. Existing proposals and implementations suggest a bruteforce approach for FDD designs in order to remove the inter-stagefilter. However, such an approach may result in higher power consumptionbecause of a higher mixer linearity and a higher level of complexity incalibration needed in smaller line width processes (e.g., 90 nm or less)due to larger variations in order to ensure performance in the presenceof the transmit leak-over signal.

Accordingly, an improved system and method for transmitter leak-overcancellation are needed.

SUMMARY

In one embodiment, a method comprises transmitting a first signal via atransmit chain in a wireless device, wherein a first portion of thefirst signal leaks over into a receive chain of the wireless device andgenerates higher order products that interfere with a second signalbeing received by the wireless device. A second portion of the firstsignal is diverted from the transmit chain into cancellation circuitrycoupled to the receive chain, wherein the second portion is divertedprior to a location in the transmit chain where leak-over occurs. Anamplitude and phase of the second portion are manipulated and themanipulated second portion is combined with the second signal to atleast partially cancel interference caused by the first portion leakingover into the receive chain.

In another embodiment, a method comprises transmitting a first signalvia a transmit chain in a wireless device, wherein a first portion ofthe first signal leaks over into a receive chain of the wireless deviceand generates higher order products that interfere with a second signalbeing received by the wireless device. A second portion of the firstsignal diverted from the transmit chain is directed into cancellationcircuitry coupled to the receive chain. An amplitude and phase of thesecond portion are manipulated before combining the manipulated secondportion with the second signal and first portion to at least partiallycancel interference caused by the first portion.

In yet another embodiment, a circuit comprises a duplexer coupling aportion of a transmit chain and a receive chain in a wireless devicethat uses separate frequency channels for simultaneous transmission andreception, wherein the duplexer is configured to isolate a transmittedsignal in the transmit chain from a received signal in the receivechain. A directional coupler is coupled to the transmit chain andconfigured to divert a portion of the transmitted signal from thetransmit chain to amplitude and phase matching circuitry. Amplitude andphase matching circuitry is coupled to the receive chain and thedirectional coupler, wherein the amplitude and phase matching circuitryincludes circuitry configured to manipulate the diverted portion tocreate destructive interference for a portion of the transmitted signalthat leaks over into the receive chain.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a block diagram of one embodiment of a portion of a wirelesscommunications device having leak-over cancellation functionality.

FIG. 2 is a flowchart illustrating one embodiment of a method forminimizing leak-over that may be performed in the device of FIG. 1.

FIG. 3 is a block diagram of another embodiment of a portion of awireless communications device having leak-over cancellationfunctionality.

FIG. 4 is a block diagram of one embodiment of a leak-over cancellationcircuit that may be used in the wireless communications device of FIG.3.

FIG. 5 is a block diagram of another embodiment of a portion of awireless communications device having leak-over cancellationfunctionality.

FIG. 6 is a block diagram of yet another embodiment of a portion of awireless communications device having leak-over cancellationfunctionality.

FIG. 7 is a flowchart illustrating one embodiment of a method forminimizing leak-over in the device of FIG. 6.

FIGS. 8A and 8B are graphs illustrating one embodiment of a receivechain low noise amplifier's (LNA) output leak-over spectrum and theLNA's output cross-modulation spectrum, respectively, withoutcancellation of the transmit leak-over.

FIGS. 9A and 9B are graphs illustrating one embodiment of a receivechain low noise amplifier's (LNA) output leak-over spectrum and theLNA's output cross-modulation spectrum, respectively, with cancellationof the transmit leak-over using a first cancellation circuitryconfiguration.

FIGS. 10A and 10B are graphs illustrating another embodiment of areceive chain low noise amplifier's (LNA) output leak-over spectrum andthe LNA's output cross-modulation spectrum, respectively, withcancellation of the transmit leak-over using the cancellation circuit ofFIG. 4.

FIGS. 11A and 11B are graphs illustrating yet another embodiment of areceive chain low noise amplifier's (LNA) output leak-over spectrum andthe LNA's output cross-modulation spectrum, respectively, withcancellation of the transmit leak-over using variations of thecancellation circuit of FIG. 4.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Referring to FIG. 1, in one embodiment, a circuit 100 includes circuitryfor minimizing or eliminating leak-over from a transmission portion ofthe circuit (i.e., a transmit (TX) chain) to a reception portion of thecircuit (i.e., a receive (RX) chain). Both transmitted and receivedsignals pass through a duplexer 102 coupled to an antenna 104. Theduplexer 102 may contain one or more filters (not shown) for isolatingthe transmit chain from the receive chains. In operation, a small partof the signal being transmitted may overcome the isolation filtering ofthe duplexer 102 and leak from the transmit chain into the receivechain, as indicated by Path 1. This leak-over may generate higher orderproducts that interfere with a signal being received by the circuit'sreceive chain.

In the present embodiment, the circuit 100 may include components forreducing the transmitter leak-over signal by means of destructiveinterference from the same source. To accomplish this, the circuit 100may use a feedback loop from the transmit chain to the receive chainthat manipulates the amplitude and/or phase of the signal being fed backinto the receive chain.

To form the feedback loop, a directional coupler 106 may be positionedin the transmit chain. As will be described below, the directionalcoupler 106 may be positioned so that the signal being redirected by thedirectional coupler is the same signal (i.e., has the same amplitude andphase) as that entering the duplexer 106. By using the same signalsource that causes the leak-over as the basis for cancellation, both theleak-over signal and the signal used for cancellation have the samereference for phase and amplitude.

The directional coupler 106 may feed a portion of the transmit signalinto amplitude and phase matching circuitry 108 positioned in thereceive chain as indicated by Path 2. Cancellation occurs at the LNAinput and the received signal may then be passed onto the receive chainwith the leak-over portion having been minimized or eliminated.

Referring to FIG. 2, one embodiment of a method 200 for cancelling atleast a portion of a signal leaking over from a transmit chain to areceive chain in a wireless device is illustrated. The method 200 may beused with a circuit configured as described with respect to the circuit100 of FIG. 1, or with circuits having other configurations.

In step 202, a signal may be transmitted via the transmit chain in thewireless device. A portion of the transmitted signal may leak-over intothe receive chain of the wireless device and generate higher orderproducts that interfere with a signal received by the wireless device,as described with respect to FIG. 1. In step 204, part of thetransmitted signal may be diverted from the transmit chain intocancellation circuitry coupled to the receive chain, such as amplitudeand phase matching circuitry 108 of FIG. 1. The diversion may occurusing a mechanism such as the directional coupler 106 of FIG. 1. Thediversion may occur prior to a location in the transmit chain where theleak-over occurs (e.g., before the transmitted signal enters theduplexer 102 of FIG. 1). In step 206, an amplitude and phase of thediverted signal may be manipulated so that the diverted signal cancancel with at least a portion of the leak-over interference. In step208, this manipulated signal is combined with the received signal to atleast partially cancel interference caused by the leak-over of thetransmitted signal into the receive chain.

Referring to FIG. 3, in another embodiment, a circuit 300 includescircuitry for minimizing or eliminating leak-over from a transmissionportion of the circuit (i.e., a transmit chain) to a reception portionof the circuit (i.e., a receive chain). For example, the circuit 300 maybe a more detailed embodiment of the circuit 100 of FIG. 1. Bothtransmitted and received signals pass through a duplexer 302 coupled toan antenna 304. In the present example, the transmit chain may include apre-power amplifier (PPA) 306, an RF bandpass filter 308, and a poweramplifier module (PAM) 310. Additional components (not shown) of thetransmit chain may be coupled to the PPA 306. The receive chain mayinclude a low noise amplifier (LNA) 312 coupled to other components (notshown) of the receive chain. In operation, a signal being transmittedvia the transmit chain may overcome the isolation filtering of theduplexer 302 and leak from the transmit chain into the receive chain atthe input of the LNA 312, as indicated by Path 1.

In the present embodiment, at least a portion of the circuit 300 mayformed as an FDD transceiver application specific integrated circuit(ASIC) and may include components for reducing transmitter leak-oversignal at the input of the receiver LNA 312 by means of destructiveinterference from the same source. As will be described below in greaterdetail, the circuit 300 may use a feedback loop from the transmitter PAM310 output to the receiver LNA 312 input that provides the amplitude andphase manipulation to minimize or eliminate the interference. Thefeedback loop may be designed as part of or separate from thetransceiver ASIC. In the present example, the feedback loop may beachieved with relatively simple design blocks with little or no impactto the transceiver's performance.

To form the feedback loop, a directional coupler 314 may be positionedin the transmit chain between the PAM 310 and the duplexer 302. Althoughthe directional coupler 314 may be positioned elsewhere, some handsettransmitters are designed with a coupler at the output of the PAM 310for functions such as level detection and gain control, making this anideal location without requiring additional design changes. Furthermore,this may be an ideal tap off point since the next block downstream isthe duplexer 302, which is designed to isolate the transmit signal fromthe receive chain. By using the illustrated position of the directionalcoupler 314, the output of the PAM 310 (which is the source of theleak-over signal) may be used as the basis for phase cancellation at theinput of the LNA 312 in the receive chain. As the same source (i.e., thePAM 310) causes the leak-over and forms the basis for the cancellation,both the leak-over signal and the signal used for cancellation have thesame reference for phase and amplitude.

The directional coupler 302 may feed a portion of the transmit signalinto amplitude and phase matching circuitry 316, which is positioned inthe receive chain between the duplexer 302 and the LNA 312, as indicatedby Path 2. Cancellation of the leak-over signal may occur at the LNAinput, and a received signal may then be passed onto the LNA 312 withthe leak-over portion having been minimized or eliminated.

With additional reference to FIG. 4, one embodiment of the amplitude andphase matching circuitry 316 of FIG. 3 is illustrated. In the presentexample, the amplitude and phase matching circuitry 316 includes aninverting buffer 400, one or more fixed or variable capacitors 402, andone or more fixed or variable resistors 404. It is understood that insome embodiments the capacitors and/or resistors may be organized incapacitive and resistive networks, respectively, in order to provideflexibility in the configuration of the circuitry 316. In operation, theredirected signal (indicated by Path 2) enters the inverting buffer 400,capacitor 402, and resistor 404 of the amplitude and phase matchingcircuitry 316, and exits as a signal having equal amplitude but theopposite phase as that of the leak-over signal (Path 1). The invertedsignal may then be mixed with the Path 1 signal and the resultingdestructive interference caused by the inverted signal may minimize oreliminate the leaked over signal.

In some embodiments of the circuit 300, it may be feasible to design theamplitude and phase matching circuitry 316 for cancellation becausevariation of the parameters for Path 1 and Path 2 may be relativelysmall during operation, which may enable an initial calibration to beperformed. Otherwise, the design variations of the amplitude and phasematching circuitry 316 (e.g., resistor and capacitor values) may be moretolerable for systems like wideband code division multiple access(WCDMA), where the amount of transmit leak-over reduction to be removedmay be less than approximately 5dB to exclude the use of an inter-stageSAW filter.

In embodiments where the directional coupler 314 is external to thetransceiver ASIC, the amplitude and phase properties are generallyspecified and may be relied upon for design of the feedback loop. Ifexternal components like the duplexer 302 exhibit relatively widevariations from part to part (i.e., different duplexers exhibitdifferent characteristics), a one time calibration of the amplitude andphase matching circuitry 316 may be performed, such as during a transmitpower calibration at the device (e.g., phone) level. In someembodiments, one or more of the inverting buffer 400, capacitors 402,and/or resistors 404 may be controllable by a processor coupled to theamplitude and phase matching circuitry 316, and the feedback loop may bedynamically controlled. In other embodiments, the feedback loop may bedynamically controlled using an analog or digital closed-loop controlmechanism, as described with respect to FIG. 6.

It is understood that receive band noise from the transmitter may alsobe fed into the input of the LNA 312 using the described feedback loop,but the duplexer 302 generally offers much lower isolation at thereceive band than the transmit band. Accordingly, with the sameattenuation in Path 2, the receive band noise may be significantly lowerthan what is leaked over into Path 1. However, some embodiments mayinclude a filter in the feedback path to provide more receive bandrejection.

The phase manipulation of the amplitude and phase matching circuitry 316may be accomplished using resistor and capacitor values that are chosenbased upon the phase adjustments required from −180 degrees as specifiedby the following equations:

H(jω)=R−j1/ωC   (Equation 1)

or in rectangular form as

|H(jω)|=SQRT(R̂2+1/(ωC)̂2)   (Equation 2)

Phase=−arctan(1/(ωRC))   (Equation 3)

where j is SQRT(−1), ω is the normalized frequency, H(jω) is thefrequency response of the system H( ), R is the resistive value, and Cis the capacitive value. Accordingly, by adjusting C with apre-determined R value, the phase of the feedback loop can bemanipulated. The inverting buffer 400 may provide the −180 degreeinversion. Using a relatively high value resistor 404 at the input ofthe LNA 312 tap-in point may serve to minimize the impedance matchingimpact on the LNA. The amplitude and phase matching circuitry 316 mayvary the amplitude of the feedback loop by adjusting the gain of theinverting buffer 400.

Referring to FIG. 5, in another embodiment, the circuit 300 of FIG. 3 isillustrated with a transmit gain comparator 500. It is understood thatthe signal provided by Path 2 may be used for many different purposesand that the signal comparison provided by the gain comparator 500 isonly one example.

Referring to FIG. 6, in yet another embodiment, the circuit 300 of FIG.3 is illustrated with closed loop control functionality to optimize theleak-over cancellation process described with respect to FIG. 3. Theclosed loop signal may follow a signal path indicated by Path 3. In thepresent example, the signal for the closed loop functionality may beprovided by tapping the received signal after the signal passes througha mixer 600 coupled to the output of the LNA 312 in the receive chain tobring the signal down to baseband for low frequency processing. Theclosed loop control functionality may be provided by an analog todigital converter (ADC) 602, a filter (e.g., a finite impulse responsefilter) 604, a power level detector 606, and a comparator 608. The ADC602 may receive the tapped signal and the comparator 608 may provide thecontrol signals to the amplitude and phase matching circuitry 316.

Although not shown, a digital to analog converter (DAC) may bepositioned in the closed loop (e.g., between the comparator 608 andamplitude and phase matching circuitry 316) to convert the digitalsignal into an analog signal. For example, if the amplitude and phasematching circuitry 316 is analog, the DAC may be used. Although thepresent embodiment illustrates a digital closed loop control mechanism,it is understood that the closed loop control functionality may beprovided using analog components or using a mixture of digital andanalog components.

To optimize the cancellation functionality provided by the amplitude andphase matching circuitry 316, the level of the transmit leak-over may bedetected and the closed loop control mechanism may be used to adjust thephase and amplitude of the feedback loop. The detection may be performedin the digital domain where a carrier signal can be effectively filteredout to isolate the transmit leak-over portion of the signal. The phaseand amplitude of the feedback loop may then be adjusted (e.g., bystoring one or more values in a register to alter the configurations ofthe inverting buffer 400, capacitor 402, and/or resistor 404 of FIG. 4)to get the detectable transmit leak-over level below a preset threshold.Since it is the relative level of the detected transmit leak-over beingcompared to the threshold, only a small amount of the signal need betapped from the main receive chain for detection. It is understood thatthe threshold may be preset to a level of transmit leak-over that issuitable for the receive chain.

Accordingly, the received signal, after cancellation of all or a portionof the leak-over has occurred, passes through the mixer 600. A portionof the received signal enters the rest of the receive chain, whileanother portion enters the ADC 602 and is converted into a digitalsignal. After conversion, the signal passes through the filter 604,which isolates the leak-over portion of the signal and passes theisolated leak-over portion to the power level detector 606. The powerlevel detector 606 measures the signal strength of the leak-overportion. The output of the power level detector 606 enters thecomparator 608, which compares the power level detector's output to athreshold. The output of the comparator 608 is fed back into theamplitude and phase matching circuitry 316 and may be used to modify howthe diverted signal received from the directional coupler 314 ismanipulated. For example, the closed loop control circuit may vary theamplitude by adjusting the gain of the inverting buffer 400 (FIG. 4) andmay tune the phase by changing the overall capacitance (e.g., byswitching embedded capacitors of a capacitor network).

Referring to FIG. 7, one embodiment of a method 700 for optimizing aleak-over cancellation circuit is illustrated. The method may be usedwith a circuit configured as described with respect to the circuit 600of FIG. 6, or with circuits having other configurations.

In step 702, a signal may be transmitted via a transmit chain in awireless device, where a portion of the signal leaks over into a receivechain of the device and interferes with a signal being received by thedevice. In step 704, the received signal, the leak-over portion, and adiverted portion of the transmitted signal may be directed intocancellation circuitry (e.g., the amplitude and phase matching circuitry316 of FIG. 4) to manipulate the diverted portion before combining thediverted portion and the received signal. In step 706, a remainder ofthe leaked signal not cancelled by the manipulated portion may befiltered from the received signal. In steps 708 and 710, respectively, apower level of the remainder may be detected and compared to a thresholdvalue. In step 712, at least one of an amplitude and phase of thecancellation circuitry may be altered based on a result of thecomparison.

Referring to FIGS. 8A and 8B, graphs 800 and 810 illustrate simulationresults of one embodiment of a receive chain LNA's (e.g., the LNA 312 ofFIG. 3) output leak-over spectrum and the LNA's output cross-modulationspectrum, respectively, without cancellation of the transmit leak-over.In the present example, the simulation model used a WCDMA FDD Uplinkgenerator to emulate the transmitter output from the PPA 310 and used aSAW filter block to emulate duplexer transmit band rejection. FIG. 8A,which includes an x-axis 802 representing the frequency in MHz and ay-axis 804 representing dB, illustrates the transmit signal spectrum 806at the LNA output without cancellation. FIG. 8B, which includes anx-axis 812 representing the frequency in MHz and a y-axis 814representing dB, illustrates the cross-modulation product 816 between aCW tone and the transmit leak-over modulated interferer at the LNAoutput without cancellation.

Referring to FIGS. 9A and 9B, graphs 900 and 910 illustrate simulationresults of one embodiment of the receive chain LNA's (e.g., the LNA ofFIGS. 8A and 8B) output leak-over spectrum and the LNA's outputcross-modulation spectrum between a CW tone and the transmit leak-overmodulated interferer, respectively, with cancellation of the transmitleak-over. In the present example, the simulation model used a capacitorvalue of 0.125 pF, a resistor value of 1.5 kΩ, feedback power at the LNAinput of −30 dBm, and a phase shift of −225.4 degrees. FIG. 9A, whichincludes an x-axis 902 representing the frequency in MHz and a y-axis904 representing dB, illustrates the transmit signal spectrum 906 at theLNA output with cancellation using cancellation circuitry configuredusing the above values. FIG. 9B, which includes an x-axis 912representing the frequency in MHz and a y-axis 914 representing dB,illustrates the cross-modulation product 916 between the CW tone and thetransmit leak-over modulated interferer at the LNA output with the sameconfiguration of the cancellation circuitry.

Referring to FIGS. 10A and 10B, graphs 1000 and 1010 illustratesimulation results of one embodiment of a receive chain LNA's (e.g., theLNA of FIGS. 8A and 8B) output leak-over spectrum and the LNA's outputcross-modulation spectrum, respectively, with cancellation of thetransmit leak-over. In the present example, the simulation model used acapacitor value of 0.2 pF, a resistor value of 1.5 kΩ, feedback power atthe LNA input of −30 dBm, and a phase shift of −212.4 degrees. FIG. 10A,which includes an x-axis 1002 representing the frequency in MHz and ay-axis 1004 representing dB, illustrates the transmit signal spectrum1006 at the LNA output with cancellation using cancellation circuitryconfigured using the above values. FIG. 10B, which includes an x-axis1012 representing the frequency in MHz and a y-axis 1014 representingdB, illustrates the cross-modulation product 1016 between the CW toneand the transmit leak-over modulated interferer at the LNA output withthe same configuration of the cancellation circuitry.

Referring to FIGS. 11A and 11B, graphs 1100 and 1110 illustratesimulation results of one embodiment of a receive chain LNA's (e.g., theLNA of FIGS. 8A and 8B) output leak-over spectrum and the LNA's outputcross-modulation spectrum, respectively, with cancellation of thetransmit leak-over. In the present example, the simulation model used acapacitor value of 0.25 pF, a resistor value of 1.5 kΩ, feedback powerat the LNA input of −30 dBm, and a phase shift of −206.9 degrees. FIG.11A, which includes an x-axis 1102 representing the frequency in MHz anda y-axis 1104 representing dB, illustrates the transmit signal spectrum1106 at the LNA output with cancellation using cancellation circuitryconfigured using the above values. FIG. 11B, which includes an x-axis1112 representing the frequency in MHz and a y-axis 1114 representingdB, illustrates the cross-modulation product 1116 at the LNA output withthe same configuration of the cancellation circuitry.

It is noted that the effects of cancellation may vary depending on thephase setting and the phase setting may manipulated by adjusting thecapacitance in the cancellation loop as explained previously.Furthermore, simulation results show that the receiver LNA performancemay remain unaffected, as can be seen by the CW tone level at theoutput, while the transmit spectrum and the corresponding crossmodulation product may be reduced using a cancellation loop as describedabove.

Although the present disclosure illustrates the cancellation circuitryas being implemented in hardware, it is understood that some or all ofthe cancellation circuitry and the functions described herein may beimplemented in software, hardware, or a combination of software andhardware. Accordingly, the specific circuit configurations describedherein are for purposes of example only and are not intended to limitthe invention.

Although only a few exemplary embodiments of this disclosure have beendescribed in details above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this disclosure. Also, features illustrated and discussedabove with respect to some embodiments can be combined with featuresillustrated and discussed above with respect to other embodiments. Forexample, various steps from different flow charts may be combined,performed in an order different from the order shown, or furtherseparated into additional steps. Furthermore, steps may be performed bynetwork elements other than those disclosed. Accordingly, all suchmodifications are intended to be included within the scope of thisdisclosure.

1. A method comprising: transmitting a first signal via a transmit chainin a wireless device, wherein a first portion of the first signal leaksover into a receive chain of the wireless device and generates higherorder products that interfere with a second signal being received by thewireless device; diverting a second portion of the first signal from thetransmit chain into cancellation circuitry coupled to the receive chain,wherein the second portion is diverted prior to a location in thetransmit chain where leak-over occurs; manipulating an amplitude andphase of the second portion; and combining the manipulated secondportion with the second signal and the first portion to at leastpartially cancel interference caused by the first portion leaking overinto the receive chain.
 2. The method of claim 1 further comprisingperforming a calibration of the cancellation circuitry.
 3. The method ofclaim 2 wherein the calibration is performed during a transmit powercalibration of the wireless device.
 4. The method of claim 2 wherein thecalibration is performed between the wireless device and anotherwireless device during production calibration of the wireless device. 5.The method of claim 1 wherein manipulating the phase of the secondportion includes inverting the phase.
 6. The method of claim 5 whereininverting the phase includes passing the second portion through aninverting buffer.
 7. The method of claim 6 wherein manipulating theamplitude includes altering at least one of a gain of the invertingbuffer and a resistor value.
 8. The method of claim 5 whereinmanipulating the phase includes adjusting at least one of a capacitorvalue and a resistor value within the cancellation circuitry.
 9. Themethod of claim 1 wherein no calibration is performed if an amount ofcancellation needed is less than a predefined threshold of decibels. 10.A method comprising: transmitting a first signal via a transmit chain ina wireless device, wherein a first portion of the first signal leaksover into a receive chain of the wireless device and generates higherorder products that interfere with a second signal being received by thewireless device; directing a second portion of the first signal divertedfrom the transmit chain into cancellation circuitry coupled to thereceive chain; and manipulating an amplitude and phase of the secondportion before combining the manipulated second portion with the secondsignal and first portion to at least partially cancel interferencecaused by the first portion.
 11. The method of claim 10 whereinmanipulating the phase of the second portion includes inverting thephase.
 12. The method of claim 11 wherein manipulating the amplitudeincludes altering at least one of a gain of the inverting buffer and aresistor value.
 13. The method of claim 11 wherein manipulating thephase includes adjusting at least one of a capacitor value and aresistor value within the cancellation circuitry.
 14. A circuitcomprising: a duplexer coupling a portion of a transmit chain and areceive chain in a wireless device that uses separate frequency channelsfor simultaneous transmission and reception, wherein the duplexer isconfigured to isolate a transmitted signal in the transmit chain from areceived signal in the receive chain; a directional coupler coupled tothe transmit chain and configured to divert a portion of the transmittedsignal from the transmit chain to amplitude and phase matchingcircuitry; and amplitude and phase matching circuitry coupled to thereceive chain and the directional coupler, wherein the amplitude andphase matching circuitry includes circuitry configured to manipulate thediverted portion to create destructive interference for a portion of thetransmitted signal that leaks over into the receive chain.
 15. Thecircuit of claim 14 wherein the directional coupler is positioned in thetransmit chain between the duplexer and a power amplifier, wherein theoutput of the power amplifier is fed into the duplexer.
 16. The circuitof claim 14 wherein the amplitude and phase matching circuitry ispositioned between the directional coupler and an input of a low noiseamplifier, wherein the output of the amplitude and phase matchingcircuitry is fed into the input of the low noise amplifier.
 17. Thecircuit of claim 16 wherein the amplitude and phase matching circuitryincludes an inverted buffer, at least one capacitor block of variablecapacitance, and at least one resistor block of variable resistanceconfigured to substantially invert a phase and vary an amplitude of thediverted portion.
 18. The circuit of claim 17 wherein a value of theresistor is selected to minimize an impact to a return loss of the inputof the low noise amplifier.
 19. The circuit of claim 14 furthercomprising a filter positioned between the directional coupler and theamplitude and phase matching circuitry, wherein the filter is configuredto remove interference caused by the received signal leaking over intothe transmit chain.
 20. The circuit of claim 14 further comprising afilter positioned between the directional coupler and the amplitude andphase matching circuitry, wherein the filter is configured to reducetransmit chain receiver band noise and spurious leaking over into thereceiver chain.
 21. The circuit of claim 14 wherein the wireless deviceis configured to use frequency division duplexing.